Aircraft heater control apparatus



Nov. 13 1945. l.L H. LESLIE, 2D v '2,383,355

` AIRCRAFT HEATER CONTROL APPARATUS Filed March 6, 1942 FUEL SUPPLY Patented Nov. 13, 1945 STATES TENT FFICE AIRCRAFT HEATER CONTROL APPARATUS Application March 6,1942, Serial No. 433,651

8 Claims.

My invention relates generally to heater control apparatus, and is more particularly concerned with the provision of an improved electrical control apparatus for aircraft heaters of the internal combustion type. y

It is an object of my invention to provide an improved control circuit and apparatus whereby the supply of fuel to the heater is automatically cut of upon overheating or prolonged failure of combustion, but which will not cut off the supply of fuel upon a temporary failure of combustion.

A further object is to provide an improved heating system in which perforation or destruction of the fuel supply conduit or exhaust conduit will result in cutting oil the fuel supply.

A further object is to provide an improved heating system for aircraft and the like in which an interruption in the current supply will result in cutting off the supply of fuel to the heater.

A further object is to provide an improved electrical control systemfor internal combustion type heaters particularly adapted for use on aircraft.

Other objects will appear from the following description, reference being had to the accom panying drawing, in which the ligure is a diagram showing the improved control circuits and apparatus. i

The control apparatus of my invention .is adapted to be used in conjunction with heaters of the internal combustion type, such as disclosed in the co-pending application oi Henry J. DeN. McCollum, Serial No. 378,262, filed February 10, 1941, which has matured into Patent No. 2,379,017.

The heater itself is indicated by the block l@ and is supplied with a combustible mixture of fuel and air through a conduit i2, and the prod.- ucts of combustion are discharged therefrom through a conduit it. For purposes of illustration, the combustible mixture is shown as being supplied from the engine supercharger i6, the now being controlled by a resiliently closed valve i8 adapted to be opened upon energization of a solenoid i9, while the discharge conduit is illustrated as connected to the intake pipe il located between the engine carburetor i and the supercharger lli. The combustible mixture supplied to the heater it is ignited therein by a resistance wire igniter 2U shown diagrammatically as having one terminal thereof connected to ground and its other terminal connected to a'conductor 22.

The electrical control system is preferably energized from the electrical generating system of the aircraft, usually at 24 volts, through a pair of supply conductors 251, 26, the latter being indicated as connected to ground. A fuse 2li and manually operable on-oil switch 30 are connected to the conductor 24, the switch 30, when closed, connecting the conductor 2t to a conductor 2l.

In the form oi' the invention shown in the iigure, there are three thermostatically operated switches responsive to the temperature of the heater I Il, namely, an S. P.'D. T. cold switch 32, an S. P. D. T. igniter switch 3, and an S. P. S. T. overheat switch 36. Each of these switches is shown in the drawing in its cold position. While the switches are illustrated as simple bimetal switches, in actual practice each will comprise a suitable snap type microswitch having its movable part snap-actuated by a temperature responsive bimetal, so that the various circuits controlled by these switches may be opened and closed without undue arcing at the points of contact. Furthermore, with this type of switch, there is some difference between the temperatures at which the switch opens and closes.

In addition to the thermostatically operated switches, there is provided a relay 38, having an S. P. D. T. switch 39, an S. P. S. T. switch t0, and a coil iii, and a relay t2 having S. P. D. T. switch i3 and coil et. A warning signal lamp t6 has one terminal connected to ground and its other terminal connected to a conductor at.

Assuming that the heater is cold and the switch 3i! is closed, current will flow through the switch 3H, conductor 2l, and switch 3d, to conductor Ell, through switch 39 to conductor 22, and hence through the electrical igniter 2li to ground. Current will also flow through a conductor 52 and switch t3 to the winding i9 of the solenoid valve It and thence to ground, thereby causingenergization of said solenoid and opening the valve it. Thus, the combustible mixture will flow from the supercharger it past the valve iB, through the conduit I2, to the combustion chamber of the heater, where, after a short time, it will be ignited by the igniter 2B., v

As the temperature of the heater rises to a value approaching its normal operating temperature, the igniter switch 36 will snap from the position shown to its opposite position, in which it will connect conductor 26 with conductor 5t, and thereby complete a circuit through the coil fil of relay 38 to energize the latter. Upon such operation of the relay 38, its switch 39 will break the (then open) circuit between conductorsll and 22, and make a circuit between said conductor and a conductor 56, the latter being connected to the cold switch 32. Energization of the relay 38 will also result in establishing a holding circuit through the winding 4I by virtue of the closure of switch 40. It will thus be seen that the relay 36 will thereafterremain energized as long as the switch 30 remains closed.

If, after the heater has attained its normal operating temperature, its temperature should, for some unforeseen accidental condition, rise materially above its normal operating temperature, the thermostatic switch 36 will close, thus establishing a circuit from the conductor 52 to the conductor 48 and complete a circuit to the warning signal lamp 46 and to the winding of relay 42. The lamp 46 will be located in a position where the attention of. the pilot or the navigator will be attracted by its illumination, and thus apprize him of the fact that the heater is not operating properly. kEnergization of the relay 42 will cause the switch 43 to open the circuit from the conductor 52 through the solenoid winding I9, whereupon, the valve I6 will close, under the influence of its spring, and shut od the supply of combustible mixture to the heater. Energization of the relay 42 will also establish a holding circuit through its coil 44 as well as result in connecting the conductor 48 to the conductor 52 so that the signal lamp 46 will remain illuminated, and the solenoid I6 will remain energized until the switch 30 is manually opened to deenergize the system. The heater will thus be prevented from operation even after it. has cooled and the overheat switch 36 has returned to cold position.

If, after normal operation of the heater has commenced and, for some reason or other, the heater cools oi, as for example, if either oi theconduits I2 or' I4 is perforated or severed by a bullet, the heater will rapidly cool so as to cause the thermally operated switches 32 and 34 to resume the positions in which they are shown in the drawing, the cold switch 32 being the last to return to its cold position illustrated. When the switch 32 does move to this position, it completes the following circuit: From switch 30 through conductor 21, ignition switch 34, conductor 50, switch 3S, conductor 56, cold switch 32, and conductor 48 to the signal lamp 46 and the coil 44 of relay 42. Energization of the relay 42 will result in deenergization of the solenoid I9 so that the valve will close and stop the ow of the combustible mixture into the conduit I2, the signal lamp 46 indicating to the operator of the vehicle that the heater is not operating properly.

The igniter switch 34 moves from it hot position to its cold position at a higher temperature than the cold switch 32 moves from its hot to its cold position. Thus, if for any reason, the flame in the heater becomes extinguished, as by temporary interruptionin the fuel mixture. supply, the igniter switch will move to its cold psition while the cold switch 32 isstill in its hot position. Under these circumstances, current will be supplied to the igniter 20 for a short period of time through the following circuit: From switch 3D throughconductor 2l, igniter switch 34, conductor 50, switch 33, conductor 56, cold switch 32, a portion of the conductor 22 and igniter 20, to ground. Thus, if the interruption of the fuel supply is of a temporary character, it will, upon recommencement ofilow into the heater, again be ignited by the igniter 20, and such ignition will, of course, result in a rise in temperature of the heater 26 so that the cold switch 32 will remain in its hot position and eventually the igniter switch l34 will move to its hot position and thereby deenergize the igniter 20.

However, if the interruption in the supply of fuel mixture to the heater is oi extended duration, the cold switch 32 will snap to its cold position and thereby complete the previously described circuit to the signal'lamp 46 and relay winding 44, completely to deenergize the heater and to cause closure of the valve I8. Thereafter, the heater can be rendered operative again only by opening the manually operated switch 30 to permit the relays 38 and 42 to resume their normal positions,k and then reclosing the switch 30, whereupon, if the fault which vcaused the operation of the heater to fail has been corrected, the heater will recommence operation as initially described.

From the foregoing, it will appear that I have provided an improved control circuit and apparatus particularly useful in aircraft heating systems which is effective to assure safe operation of the system under allv adverse conditions and have devised a simplified and modified circuit and apparatus which assures safe operation of the heater under most of the adverse conditions which may be encountered.

While I have shown and described a particular form of my invention, it will be apparent to those skilled in the art that numerous variations and modiflcations may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention such variations and modifications by which substantially the results of my invention may be obtained by the use of substantially the same or equivalent means.

I claim:

l. In an aircraft heating system having an internal combustion type heater provided with electrical ignition means and means to supply a fuel mixture thereto, the combination of a valve for controlling the Supply of fuel mixture to the heater electromagnetic means energized to maintain said valve in open position while .the heating system is in normal operation, a circuit for supplying electrical energy to said electrical igniter, a temperature responsive igniter switch in said circuit effective to open the same when the heated attains its substantially normal operating temperature and to close said circuit when the heater drops slightly below said temperature, a cold switch responsive to the temperature of said heater and operated upon attainment of a temperature lower than that required to close said igniter switch, and means controlled jointly by said cold switch and said igniter switch to deenergize said electromagnetically operated valve when both of said switches are in their cold positions.

2. The combination set forth in claim l in which means are provided to prevent deenergization of said electromagnetically operated valve by said cold switch until a. time subsequent to the attainment of substantially normal operating temperature by said heater.

3. The combination set forth in claim 1 in which the means for deenergizing the electromagnetically operated valve includes a relay energized upon closure of said cold switch.

4. The combination set forth in claim l in which there is provided a temperature responsive overheat switch and means associated therewith to effect closure of said electromagnetically operated valve upon the occurrence of an overheat condition in said heater.

5. -In an aircraft heating system having an internal combustion type heater provided with a combustible mixture supply conduit and means for conveying the products of combustion therefrom, a valve in said conduit, an electrical igniter in said heater, electromagnetic means for operating said valve, said means maintaining said valve open while the heating system is in normal operation, means supplying energizing current to said igniter including a thermal igniter switch, a thermal cold switch, a relay having a holding circuit, a circuit completed by said igniter switch when the temperature of said heater drops below a predetermined value to energize said relay and thereby establish its'holding circuit, a s witch closed upon energization of said relay, and a circuit including said relayclosed switch and said cold switch and operable upon completion to eiect closure of said valve by deenergizing said electromagnetic means.

6. In an aircraft heating system, the combination of an internal combustion type'heater including means for supplying a combustible mixture thereto and for withdrawing the products of combustion therefrom, a valve for controllingv the ow of combustible mixture to said heater, electromagnetic means for maintaining said valve open while the system is in normal operation, an igniter switch, a cold switch, an electrically energized igniter for igniting the fuel in said heater, temperature responsive means for operating said switches, the temperature responsive means for said cold switch operating at lower temperatures than the temperature responsive means for said igniter switch, means for renderlng said cold switch ineffective as the temperature of said heater increases from room temperature to its normal operating temperature, electrical means controlled by said igniter switch to render said cold switch effective, means to lock said last named means in position rendering said cold switch eiective, and means operated by said cold switch upon a decrease in temperature -of said heater substantially below its normal operating temperature to eiect closure of said valve through deenergization of said electromagnetic mealnS.

JOHN H. LESLIE, II. 

